This invention relates generally to internal combustion engines for propelling motor vehicles, and particularly to fueling strategies for such engines. More specifically it relates to a strategy for limiting fueling after an engine retarder that had been activated to slow an engine by augmenting back-pressure on the engine has been deactivated to discontinue the augmentation of back-pressure.
A known technique for retarding an internal combustion engine comprises augmenting engine back-pressure. One way of doing this comprises restricting the exhaust gas flow from the engine. In a conventional camshaft engine, a valve that is disposed in the exhaust system, sometimes called an exhaust brake, can be operated to restrict the exhaust gas flow. In an engine that has variable valve actuation, the individual cylinder exhaust valves may be actuated in a manner that creates tho desired restriction.
Certain diesel engines have fuel injection systems that utilize hydraulic fluid under pressure to force fuel into engine combustion chambers. The hydraulic fluid is supplied to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber.
The present invention arises out of the observation that when engine retarding is accompanied by an increase in pressure of the hydraulic fluid used to force fuel into engine combustion chambers, the pressure may be undesirably high when the retarding ends. Such a condition can lead to undesirable effects in the combustion chambers, such as poor combustion quality and even misfire. In turn, such effects can adversely impact tailpipe emissions and/or drivability of the motor vehicle being propelled by the engine.
The present invention is directed toward a solution for minimizing, and ideally eliminating, such consequences by employing a novel strategy in the engine control system to limit engine fueling upon deactivation of an engine retarder. Upon deactivation of the engine retarder, the strategy immediately shuts off fueling and keeps the fueling shut off so long as the difference between a desired pressure for the hydraulic fluid used to force fuel into the combustion chambers and actual pressure of the hydraulic fluid equals or exceeds a value correlated both with the speed at which the engine is running and with governed engine fueling appropriate for the load on the engine at the engine running speed. Once the difference between the desired hydraulic fluid pressure and actual hydraulic fluid pressure ceases to equal or exceed a value correlated both with engine running speed and with governed engine fueling appropriate for the engine load at the engine running speed, the control system begins to increase the limit value. A map of fueling limit values versus time is used to increase the limit value as a function of time.
Accordingly, one generic aspect of the present invention relates to an internal combustion engine comprising a fueling system that uses hydraulic fluid for forcing fuel into engine combustion chambers and an engine control system for controlling various aspects of engine operation including fueling of the engine combustion chambers by the fueling system and the pressure of hydraulicfluid that forces fuel into the combustion chambers. The engine also comprises a mechanism for retarding the engine in consequence of the control system activating an engine retarder and for discontinuing engine retarding upon deactivation of the engine retarder.
In consequence of deactivation of the engine retarder, the engine control system initially limits engine fueling to a limit value, zero fueling is preferred, for as long as the difference between a desired pressure for the hydraulic fluid and actual pressure of the hydraulic fluid equals or exceeds a value correlated both with the speed at which the engine is running and with governed engine fueling appropriate for the load on the engine at the engine running speed. Once the difference between the desired hydraulic fluid pressure and actual hydraulic fluid pressure ceases to equal or exceed a value correlated both with engine running speed and with governed engine fueling appropriate for the engine load at the engine running speed, the control system begins to increase the limit value.
Another generic aspect relates to an internal combustion engine comprising a fueling system that uses hydraulic fluid for forcing fuel into engine combustion chambers and an engine control system for controlling various aspects of engine operation including fueling of the engine combustion chambers by the fueling system and the pressure of hydraulic fluid that forces fuel into the combustion chambers.
The engine control system comprises plural fueling limit sources providing plural fueling limits for fueling the engine, one of the fueling limit sources being effective, upon the control system deactivating an engine retarder, to impose an initial fueling limit on engine fueling and at a later time increase the fueling limit above the initial fueling limit. A minimum selection function selects the smallest valued fueling limit from the plural fueling limit sources and uses it to limit fueling.
Still another generic aspect relates to a control system for an internal combustion engine comprising a processor for processing various data to develop data for control of various engine functions, including control of hydraulic fluid pressure used by a fueling system to force fuel into engine combustion chambers and control of engine fueling. Upon the processor developing data calling for deactivation of an engine retarder that has been retarding the engine, the processor executes an algorithm that develops fueling limit data for imposing an initial limit on engine fueling, zero fueling being preferred, and at a later time increasing the limit above the initial limit.
Still another generic aspect relates to a method for limiting fueling of an internal combustion engine having a fueling system that utilizes hydraulic fluid under pressure to force fuel into engine combustion chambers when an engine retarder that had been activated to operate a mechanism for augmenting back-pressure on the engine to retard the engine is deactivated to discontinue augmenting back-pressure on the engine and hence discontinue retarding the engine. In consequence of deactivation of the engine retarder, engine fueling is initially limited to a limit value, zero fueling being preferred, as long as the difference between a desired pressure for the hydraulic fluid and actual pressure of the hydraulic fluid equals or exceeds a value correlated both with the speed at which the engine is running and with governed engine fueling appropriate for the load on the engine at the engine running speed. Once the difference between the desired hydraulic fluid pressure and actual hydraulic fluid pressure ceases to equal or exceed a value correlated both with engine running speed and with governed engine fueling appropriate for the engine load at the engine running speed, the limit value begins to be increased.
The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes drawings, now briefly described as follows.